Diastereoisomeric amino acids and derivatives are useful intermediates for preparing various pharmaceutical compounds such as enkephalinase inhibitors which are useful for treating pain or as inhibitors of the angiotensin converting enzyme (ACE) which are useful for treating hypertension or reducing elevated intraocular pressure associated with glaucoma. U.S. Pat. No. 4,652,668 discloses a process for preparing a class of pharmaceuticals useful in inhibiting angiotensin converting enzyme in humans such as N-(1-(S)-ethoxycarbonyl-3-phenylpropyl)-L-proline maleate salt is representative. German Offenlegungsschrift DE 3624376 A1 discloses a process for preparing 0-Acyl-glycosyl amines derivatives useful for preparing amino acids and derivatives by first treating an aldehyde compound with 0-acyl glycosyl amine under acidic conditions, followed by treatment with trimethylsilyl or sodium cyanide and tin or zinc (tetra)-chloride in tetrahydrofuran, isopropanol or chloroform. P. K. Subramanian and R. W. Woodward, Synth. Commun. 16 (3), pp. 337-342 (1986) disclose a four-step asymmetric Strecker synthesis for preparing (R)-(+)-2-methyl-3-phenylalanine by utilizing (S) phenylalanine as the chiral auxiliary reagent. K. Weinges, G. Graab, D. Nagel and B. Stemmle, Chem. Ber. Vol. 104 , pp. 3594-3606 (1971) disclose an external asymmetric Strecker synthesis of .alpha.-methyl-amino acids. K. Weinges, K. Gries, B. Stemmle, W. Schrank, Chem. Ber. Vol. 110, pp. 2098-2105 (1977) disclose an asymmetric Strecker synthesis with (S)-(-)-1-phenylethylamine as a chiral handle to afford stereochemically homogeneous .alpha.-methyl-.alpha.-aminonitriles. K. Weinges and B. Stemmle, Chem. Ber. Vol. 106, pp. 2291-2297 (1973) disclose an asymmetric Strecker synthesis of aliphatic .alpha.-methyl-.alpha.-amino acids. S. Inoue et al. J. Chem. Soc. Chem. Comm. 1981, pp. 229. Japan Kokai Tokkyo Koho, JP 01047754 A2 Feb. 22, 1989 Heisei, JP 87-204860 Aug. 18, 1987, CA111(13):114878h discloses a process for preparing .gamma.-1-carboxyethylamino-.gamma.-phenylbutyronitrile and .gamma.-phenylbutyric acid derivatives as intermediates for anti-hypertensive compounds. The article of K. Kawashiro, S. Morimoto and H. Yoshida, Gas chromatography-mass spectrometry of trimethylsilylated imino derivatives of alanine, Bull. Chem. Soc. Jpn., 58(7), pp. 1903-12 discloses trimethylsilylation of seven imino derivatives of alanine with N,O-bis(trimethylsilyl)trifluoracetamide in acetonitrile. It would be desirable to provide a process for preparing either (S,S) or (R,R) diastereoisomers in high optical yields which is relatively inexpensive and which does not require a protecting group for the amine starting material.